Standardized structural members are of wide utility as the building blocks of many modern structures. For example, such structural members are often used in erecting buildings and bridges. Even temporary structures such as scaffolding are now commonly erected from these structural members.
The structural members for temporary structures should meet several requirements. They should be easy to handle and of such design that a minimum number of different types of members are required for erecting a structure. Structures erected from the structural members must also be durable and stable for their intended use. For example, the dangers and difficulties of erecting sufficiently durable and stable scaffolding are so well-known as to have prompted many local regulations requiring licenses certifying those qualified to erect scaffolding.
In addition to these requirements, the temporary nature of such structures requires that the structural members and couplings used in their construction be easy to assemble and dismantle. Since the structural members are standardized, it is also desirable to have standardized devices for assembling these members. Ease of assembly dictates that the devices assembling the structural members also consist of as few different components as possible.
A variety of structural members are known. Many of these structural members are made from light metals in the shape of rails or tubes. These structural members are assembled with special couplings. For example, tubular members are familiarly assembled with sleeve couplings fitting about the tubular members and secured to the members by bolts. After repeated use, the portions of the structural members which interact with the couplings are particularly subject to undesirable deformation and wear from the tendency of the structural members to rotate relative to each other.